A liquid crystal display is a device displaying a picture by inserting liquid crystals two sheets of thin transparent substrates. In the liquid crystal display, liquid crystals change their molecular arrangement as voltage is applied via electrodes connected thereto, so that light transmission may be varied to display a picture or a color. The liquid crystal display has advantages of being low power consumption and being capable of sheeting it flat, and thus is now in the limelight of various fields.
The liquid crystal display may be classified into electrical driving scheme and optical driving scheme according to a driving scheme. A representative example of the optical driving scheme is SLM (spatial light modulator), in which the liquid crystal display is controlled by optical signals.
Meanwhile, the electrical driving scheme may be classified into passive matrix type and active matrix type depending on the presence of active elements on driving pixel electrodes.
The passive matrix type may be classified into TN-LCD (twisted nematic-LCD), STN (super twisted nematic-LCD), F-LCD (ferroelectic-LCD) and PD-LCD (polymer dispersed-LCD), according to types of liquid crystals, and the active matrix type may be classified into two terminal type and tree terminal type, according to number of terminals.
In addition, the above two terminal type generally uses MIM (metal-insulator-metal) type or diode type, and the tree terminal type generally uses thin film transistors.
The active matrix liquid crystal display has a color filter substrate (upper transparent substrate), on which common electrodes are formed; an array substrate (bottom transparent substrate), on which pixel electrode are formed; and a liquid crystal panel comprising liquid crystals interposed between said two substrates. This display is such a type that the common electrodes and the pixel electrodes drive liquid crystals by electric field applied up and down, and has excellent transmittance, aperture ratio, resolution and capability for representing moving images.
Meanwhile, to improve viewing angle characteristics, some liquid crystal displays, such as multi-domain liquid crystal display, compensation film liquid crystal display, vertical alignment liquid crystal display (VA-LCD) and in-plane switching liquid crystal display (IPS-LCD), have been developed.
The IPS mode of the above displays is suitable to large area displays such as monitors, and has an advantage that all viewing angles are wide in the left, right, top and bottom directions.
In this IPS mode, a liquid crystal panel has the upper substrate of a color filter substrate and the bottom substrate of an array substrate, which are apart from each other, and opposite to each other, and has a liquid crystal layer interposed between said upper and bottom substrates. On said upper substrate, a black matrix is formed, which serves to interrupt light leakage, in a form of matrix, and red, green and blue layers are formed, sequentially and repeatedly, at regions corresponding to pixel regions, respectively, and an overcoat layer is usually formed thereon. On said bottom substrate, common electrodes and pixel electrodes are formed, whereby the liquid crystal layer operates by horizontal electrical field with the common electrodes and the pixel electrodes.
Generally, said various liquid crystal displays have a structure as represented in FIG. 1. Specifically, the liquid crystal display has a liquid crystal panel comprising a liquid crystal layer (1) and the upper and bottom substrates (for example, a glass substrate such as a color filter substrate and an array substrate) (2-1, 2-2), and also comprises the upper polarizer (3) formed on the upper part of said liquid crystal panel and the bottom polarizer (not represented therein) formed on the bottom part thereof.
A polarizing film (or polarizing element) (3-1) included in the upper or bottom polarizer comprises a iodine-based compound or a dichroic polarizing material arranged in certain direction, and protective films (3-2, 3-3) for protecting the polarizing film are formed on the upper part and the bottom part. In addition, additionally functional films such as an antireflective film (3-4) may be formed on the polarizer.
Such a polarizer is usually attached to a liquid crystal panel via a pressure sensitive adhesive (b). Here, said upper polarizer (3) is not directly attached to the liquid crystal panel, but following first forming an ITO thin film (a) thereon, it is attached thereto.
The reason for forming the ITO thin film (a) between the liquid crystal panel and the upper polarizer is to solve problems such as malfunction of devices or stains by static electricity generated in procedures of preparing or using liquid crystal displays.
That is, much static electricity is often generated in a process of peeling off a release film on a pressure sensitive adhesive of the polarizer, to attach it to the outside surface of the liquid crystal panel, and also preparation or use procedures. Such generated static electricity affects arrangement of the liquid crystal layer to deteriorate quality of products or induce malfunction of devices. Therefore, to prevent this problem, static electricity is prevented by forming the ITO layer via vapor deposition processes using sputtering equipments and attaching the polarizer on the upper part of such formed ITO layer.
Demand for preventing such static electricity is important, particularly, in the above described IPS-LCD. That is, as both of pixel electrodes and common electrodes in the IPS liquid crystal panel are formed on only the array substrate of the bottom substrate, static electricity generation is particularly problematic in a process of attaching the polarizer to the outside surface of the upper substrate (color filter substrate).
However, with regard to said ITO, there are concerns about demand and supply difficulty and cost increase, and the like, due to depletion of raw materials in future. In addition, since equipments for vapor depositing ITO thin films are expensive, there is a problem that the unit cost of production increases.
Therefore, such an alternative that the ITO layer is not totally formed on the liquid crystal panel, but partially formed thereon, is practiced. Ultimately, it is required to develop techniques being capable to obtain the desired antistatic performance without using said ITO layer.